moves into its fourth day,presidentobamaandfirst lady michelle will arrive in town tomorrow. they'll be here for an interfaith church service to mourn the three people killed in the attacks. terry mcsweeney, nbc bay area news. >> we invite you to stay with nbc bay area news for all the latest on the developing investigation. we'll have more from boston in just a few hours on our morning show beginning at 4:30 a.m. you can get updates any time on our website at nbcbayarea.com. >>> the man who sent letters that tested positive for ricin is under arrest tonight. a law enforcement source says they arrested kenneth curtis who they believe is from tupelo, mississippi. roger wicker in mississippi received one of those letters believed to be curtis. lab tests are being conducted and results are expected in 48 hours. ricin is a highly toxic compound. >>> tonight new questions and accusations involving the 15-year-old girl who committed suicide after being allegedly sexually assaulted and bullied by three teenaged boys. they were all classmates at sarah toga high school. the los gatos schoo